The use of high-power fiber-coupled lasers continues to gain popularity for a variety of applications, such as materials processing, cutting, welding, and/or additive manufacturing. These lasers include, for example, fiber lasers, disk lasers, diode lasers, diode-pumped solid state lasers, and lamp-pumped solid state lasers. In these systems, optical power is delivered from the laser to a work piece via an optical fiber.
Various fiber-coupled laser materials processing tasks require different beam characteristics (e.g., spatial profiles and/or divergence profiles). For example, cutting thick metal and welding generally require a larger spot size than cutting thin metal. Ideally, the laser beam properties would be adjustable to enable optimized processing for these different tasks. Conventionally, users have two choices: (1) Employ a laser system with fixed beam characteristics that can be used for different tasks but is not optimal for most of them (i.e., a compromise between performance and flexibility); or (2) Purchase a laser system or accessories that offer variable beam characteristics but that add significant cost, size, weight, complexity, and perhaps performance degradation (e.g., optical loss) or reliability degradation (e.g., reduced robustness or up-time). Currently available laser systems capable of varying beam characteristics require the use of free-space optics or other complex and expensive add-on mechanisms (e.g., zoom lenses, mirrors, translatable or motorized lenses, combiners, etc.) in order to vary beam characteristics. No solution exists that provides the desired adjustability in beam characteristics that minimizes or eliminates reliance on the use of free-space optics or other extra components that add significant penalties in terms of cost, complexity, performance, and/or reliability. What is needed is an in-fiber apparatus for providing varying beam characteristics that does not require or minimizes the use of free-space optics and that can avoid significant cost, complexity, performance tradeoffs, and/or reliability degradation.
During material processing with high power lasers, a laser beam may be used to melt portions of the material which accumulates in a “melt pool.” Due to various factors, including the instability of the liquid walls of the melt pool as a function of melt pool surface tension and gravity, the melt pool itself can be rendered unstable. Such instability during melting and re-solidification can result in several detrimental effects that limit the process outcome, application-specific performance, or utility of the final product. For example, detrimental effects can include spatter (i.e., a volume of material from the melt pool which is separated from the melt pool and deposits on a surface of a material), introduction of environmental constituents into the material including gases and/or impurities, which can lead to bubbles or porosity in the re-solidified material, or an unstable melt geometry which can lead to undesirable characteristics such as grain geometry, grain size, grain orientation, morphology of the microstructure, residual stress, etc., in the re-solidified material and may affect a finished welded or additive manufactured product, including that such products may suffer from solidification cracking. Even aesthetic appearance of a final product can be affected. Each of these effects directly relate to quality and performance metrics of the laser-processed product such as strength, ductility, toughness, fatigue performance, and service life.
Manufacturing techniques that can rely on laser-melting of materials, such as additive manufacturing (also known as 3D printing) which can be used to form articles layer-by-layer and others such as laser-welding which can be used to fuse materials (e.g., different components) together, and laser-cutting for cutting through or separating materials can result in the formation of unstable melt pools leading to unwanted spatter. However, specific control of melt pool formation for example, in-real time, to tailor the material properties is limited.
Therefore, methods for controlling properties of laser-processed materials that overcome the limitations of conventional processes to provide improved articles would be a welcome addition to the art.